\documentclass[12pt]{article}
\usepackage{amssymb,amsmath,amscd,concmath,amsfonts}
\usepackage{color}
\pagestyle{empty}
\begin{document}
\begin{equation*}
  \aligned[c]
    \frac{d}{dt} \begin{bmatrix} p \\ \theta \\ \dot p \\ \dot \theta \end{bmatrix} &=
    \bmatrix \dot p \\ \dot \theta \\
      \dfrac{
        - m l \sin\theta \dot\theta^2 
        + m g (m l^2 / J_t) \sin\theta \cos\theta 
	- c \dot p \underline{- \gamma l m \cos\theta \dot\theta}
        + u}
        {M_t - m (m l^2 / J_t) \cos^2\theta  } \\[2ex]
      \dfrac{
	- m l^2 \sin\theta \cos\theta \dot\theta^2 
        + M_t g l \sin\theta 
        \underline{- c l \cos\theta \dot p - \gamma (M_t/m) \dot \theta}
	+ l \cos\theta u}
        {J_t (M_t/m) - m (l \cos\theta)^2}
    \endbmatrix \\
    y &= \begin{bmatrix}p \\ \theta \end{bmatrix}.
  \endaligned
\end{equation*}
\end{document}